Methods have been proposed in which a workpiece such as a semiconductor wafer is processed by, for example, back-grinding and photofabrication while the workpiece has been joined to a support such as a glass substrate through a temporary fixing material. Such a temporary fixing material is required to be able to temporarily fix the workpiece on the support during the processing treatment and allow the support and the workpiece to be separated easily from each other after the processing treatment.
For this separation, methods have been proposed in which radiation energy such as UV lights and infrared lights is applied to a temporary fixing material that has formed a stack together with a support and a workpiece so as to reduce the adhesion of the temporary fixing material and thereafter the support and the workpiece are separated from each other (see Patent Literatures 1 to 3). Hereinafter, the term “irradiation separation method” is used to indicate a method that separates a support and a workpiece from each other after or while a temporary fixing material is irradiated with light so as to reduce the adhesion thereof.
Patent Literatures 1 to 3 disclose temporary fixing materials for use in an irradiation separation method. The temporary fixing material of Patent Literature 1 has a bonding layer and a release layer. The temporary fixing material of Patent Literature 2 has an adhesive layer and a separation layer that contains a light-absorbing polymer. The temporary fixing material of Patent Literature 3 has a pressure-sensitive adhesive layer, a light-shielding layer and a photothermic layer.